x86/hyperv: Avoid reporting bogus NMI status for Gen2 instances

Generation2 instances don't support reporting the NMI status on port 0x61,
read from there returns 'ff' and we end up reporting nonsensical PCI
error (as there is no PCI bus in these instances) on all NMIs:

    NMI: PCI system error (SERR) for reason ff on CPU 0.
    Dazed and confused, but trying to continue

Fix the issue by overriding x86_platform.get_nmi_reason. Use 'booted on
EFI' flag to detect Gen2 instances.

Signed-off-by: Vitaly Kuznetsov <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Cathy Avery <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 4e7c6933691c..10c11b4da31d 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -152,6 +152,11 @@ static struct clocksource hyperv_cs = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static unsigned char hv_get_nmi_reason(void)
+{
+	return 0;
+}
+
 static void __init ms_hyperv_init_platform(void)
 {
 	/*
@@ -191,6 +196,13 @@ static void __init ms_hyperv_init_platform(void)
 	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
 #endif
 	mark_tsc_unstable("running on Hyper-V");
+
+	/*
+	 * Generation 2 instances don't support reading the NMI status from
+	 * 0x61 port.
+	 */
+	if (efi_enabled(EFI_BOOT))
+		x86_platform.get_nmi_reason = hv_get_nmi_reason;
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {